Why should I use system.empty in a set

GAMS
1

Hi

In the first example of the embedded code documentation, the following code is shown:

Set cc      / "France - Paris", "France - Lille", "France - Toulouse" 
              "Spain - Madrid", "Spain - Cordoba", "Spain - Seville", "Spain - Bilbao" 
              "USA - Washington DC", "USA - Houston", "USA - New York", 
              "Germany - Berlin", "Germany - Munich", "Germany - Bonn" / 
    country / system.empty / 
    city    / system.empty / 
    mccCountry(cc,country), mccCity(cc,city);

What is the reason for using /system.empty/ as it seems to work fine when I drop the /system.empty/:

    country 
    city

Cheers
Renger

2

Renger,

In general the system.empty is used to initialize an empty set and set its dimension (1 in this example) at the same time. But you are right, that it is actually not needed in this example.

Best regards,
Lutz